MHT MidSpan LP, a middle-market investment bank with offices in Boston, Dallas and San Francisco, has opened a Houston office at 4550 Post Oak Place to expand its natural resources and medical device portfolio. The bank has named Todd Graham as the Houston-area leader. Graham previously served as the managing partner of the First/Third Capital Group, a boutique investment firm, and president of SuperOx Holdings LLC, a water technology company. It is the natural resources expertise that brought Graham…